深入delphi编程理解之消息（三）发送消息函数的一般应用实例

　　通过对消息函数（SendMessage、PostMessage、Perform）的一般应用，来说明sendmessage、postmessage函数和perform 方法调用方式和结果的区别。

      一、程序界面

　二、程序代码及注释

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    procedure MyWMClose(var Amessage: TWMClose); message WM_CLOSE;   {拦截关闭窗口消息}
  end;

var
  Form1: TForm1;

implementation

uses
  CommCtrl;
{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  SendMessage(Edit1.Handle, WM_SETTEXT, 255, Integer(PChar('abc'))); {发送字符ABC}
// Edit1.Perform(WM_SETTEXT,255,Integer(PChar('abc')));
// PostMessage(Edit1.Handle,WM_SETTEXT,255,Integer(PChar('abc')));
//SendMessage(Edit1.Handle,WM_Char,Wparam('Q'),1);  {传递字符 }
end;

procedure TForm1.Button2Click(Sender: TObject);
var
 MyBroadCastMsg:cardinal;
begin
  MyBroadCastMsg:=RegeisterWindowsMessage('MyBroadCastMsg'); //向系统注册消息
  SendMessage(HWND_BROADCAST,MyBroadCastMsg,0,0); //向系统广播消息。
  //PostMessage(Button2.Handle, BM_SETSTYLE, BS_RADIOBUTTON, 1); //改变按钮风格
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
  SendMessage(Handle, WM_CLOSE, 0, 0);  {点击按钮后 ,弹出MyWMClose函数窗口，点击取消息按后才会显示“欢迎回来”窗口；}
  //Form1.Perform(WM_CLOSE, 0, 0);
 //PostMessage(Handle, WM_CLOSE, 0, 0); {点击按钮后 ,马上显示“欢迎回来”窗口，这是三个函数执行流程区别的体现。}
  ShowMessage('欢迎回来');
end;

procedure Tform1.MyWMClose(var Amessage: TWMClose);   {拦截关闭窗口消息 }
begin
  case MessageBoxW(Handle, '确认关闭窗口？', '提示', MB_OKCANCEL + MB_ICONQUESTION) of
    IDOK:
      begin
        Close;
      end;
    IDCANCEL:
      begin

      end;
  end;

end;

end.

　　分析：PostMessage函数与SendMessage函数和Perform方法主要区别在执行流程上的区别，PostMessage函数就象甩手雷，只管甩，不管是不是哑弹，可以连续甩。而SendMessage函数和Perform不仅要甩，而且要等到手雷爆炸后才能甩下一个。